Conventional unidirectional chargers consist of three stages. FIG. 1 shows a power circuit schematic 100 of the conventional charger. A first conventional stage 102 is an alternating-current-to-direct-current (AC-DC) diode-rectifier stage, a second stage 104 is a power-factor-correction stage, and a third stage 106 is an isolated direct current-to-direct current (DC-DC) converter stage.
The first stage 102 is for converting an AC, sinusoidal, current 108 into a DC rectified sinusoidal current. The second stage 104 is for shaping the input current. The third stage 106 is for regulating the output voltage 110 to be provided to the battery (not shown). The third stage 106 includes an isolation transformer 112 for galvanic isolation.
The conventional charger 100 shown can also include electro-magnetic interference (EMI) filters 114, 116 at either end of the circuit, as shown.
The charger 100 also includes a relatively large and bulky intermediate DC bus capacitor 118. The capacitor 118 is used for storing low-frequency and high-frequency ripple energy from the input line 108 for providing a pure DC output to the battery side—i.e., the capacitor 118 filters AC power to DC power. The high-frequency ripple results from required high-frequency switching, and the low-frequency ripple is due to a second harmonic frequency component at about twice the line frequency following the power-factor-correction stage 104.
The capacitor 118 can thus be viewed as acting as a stiff DC-voltage input source for the DC-DC converter 106.
Disadvantages of the conventional charger 100 include its larger size and cost, due to the bulky DC capacitor 118, and lower efficiency due to losses in the multiple stages through which power has to be processed.
Still another disadvantage of conventional chargers 100 is that they have lower reliability due to the bulky electrolytic capacitors 118. These capacitors have a limited life span due to drying out of the dielectric.
Yet another disadvantage of conventional chargers 100 is that they require two-stage control: (1) control of input current shaping and DC link voltage regulation—i.e., stabilizing voltage across the bulky DC capacitor 118, and (2) control of output voltage and current. The present invention novelly uses a single-stage control for both input current shaping and output voltage and current control, simplifying greatly the charging apparatus and process.
The above, and other disadvantages, of conventional systems are solved by the present technology.